Conventionally, radar apparatuses that transmit an electromagnetic wave by a rotating antenna and receive an echo (reflection wave) from the circumference are known. Such a radar apparatus is disclosed in JP H11-023707(A) and JP 2003-279641(A), for example.
Appropriate signal processing is applied in a signal processing device to the echo signal (hereinafter, referred to as “the reception signal”) received by an antenna. As such signal processing, for example, a gain control, an echo stretch (expansion processing of the echo), echo trail generation processing (tracking processing), and scan-to-scan correlation processing can be used.
Hereinafter, the gain control is briefly described as an example of the signal processing. That is, the reception signal may include, in many cases, signals unnecessary for an operator. For this reason, conventionally, predetermined signal processing is performed to the reception signal to suppress a signal level of the unnecessary signals (gain control).
The conventional gain control generally reduces the signal level of the unnecessary signals by performing suitable processing for the inputted reception signal, applies threshold processing, and then outputs the processed signal, for example. Here, the threshold processing outputs a signal having the signal level equal to or higher than a predetermined threshold level (otherwise, a signal having the signal level below the threshold level is not outputted). As described above, the signal can be outputted after the level of unnecessary signals is suppressed by the gain control.
However, the gain control has a disadvantage in which the signals “necessary” for the operator may also be suppressed when the unnecessary signals are excessively suppressed.
In the meantime, JP H11-023707(A) discloses a configuration in which only the reception signals from an ocean area are outputted by using electronic nautical chart information. Therefore, the necessary reception signals (signals from the ocean area) can be certainly outputted, thereby suppressing only the unnecessary reception signals (signals from a land area).
However, it is believed that the signals received by the antenna include various kinds of signals, such as signals indicating sea surface reflections, signals indicating rain-and-snow clutters, signals indicating echoes from other ships, signals indicating echoes from land, and signals indicating echoes from buoys or flag buoys.
In this regard, however, because the method of JP H11-023707(A) only distinguishes the ocean areas from the land areas based on the electronic nautical chart information, it cannot be applied to the control such as applying the gain control only to the sea surface reflections.
That is, the conventional signal processing device cannot perform flexible processing such as selecting an arbitrary kind of reception signal to perform the gain control. This is not limited only to the gain control, but the signal processing cannot be performed after the arbitrary kind of the reception signal is selected, also for the echo stretch, the echo trail generation processing, and the scan-to-scan correlation processing, etc.